Schematic overview and characterization of Darasorb cells. (A) The schematic diagram shows a pan-agglutinating plasma of a patient treated with anti-CD38 (eg, DARA). Detection of irregular antibodies (anti-RBCs) within the plasma is obscured by pan-agglutination due to anti-CD38 mAbs. Nonhuman cells expressing human CD38 at high density (here called “Darasorb” cells) deplete free medicinal antibody from patient plasma, whereas other antibodies remain unaffected. Subsequently, Darasorb cells are removed by centrifugation, whereas all other antibody species are preserved. (B) Nonhuman cells were stably transduced to coexpress human CD38 antigen and the fluorochrome Venus. CD38-expressing Darasorb cells bind DARA (labeled with Alexa Fluor 647). (C) Approximate antigen density determination was achieved with BD Quantibrite beads bearing a defined number of phycoerythrin (PE) molecules on their surface as reference. The PE molecules per cell are divided into “low,” “medium low,” “medium high,” and “high.” Cells of interest were analyzed for human CD38 surface expression with an anti-human CD38-PE antibody. Murine parental cells, Darasorb cells, and human erythrocytes are shown. A Darasorb cell displays ∼490 000 copies of CD38 compared with human erythrocytes, with ∼100 CD38 molecules per RBC. (D) Reactivity of a plasma sample from a patient treated with DARA is shown in the gel agglutination test. The untreated plasma (left panel) shows the expected agglutination in the IAT. The reaction is not sensitive to incubation with parental cells (middle panel). The same plasma treated with Darasorb cells (right panel) is devoid of reactivity, confirming quantitative depletion of DARA.